Tailoring Impact Toughness of Poly(l-lactide)/Poly(ε-caprolactone) (PLLA/PCL) Blends by Controlling Crystallization of PLLA Matrix

Abstract

Melt blending poly(L-lactide) (PLLA) with various biodegradable polymers has been thought to be the most economic and effective route to toughen PLLA without compromising its biodegradability. Unfortunately, only very limited improvement in notched impact toughness can be achieved, although most of these blends show significant enhancement in tensile toughness. In this work, biodegradable poly(ε-caprolactone) (PCL) was used as an impact modifier to toughen PLLA and a nucleating agent was utilized to tailor the crystallization of PLLA matrix. Depending on the nucleating agent concentrations in the matrix and mold temperatures in injection molding, PLLA/PCL blends with a wide range of matrix crystallinity (10-50%) were prepared by practical injection molding. The results show that there is a linear relationship between PLLA matrix crystallinity and impact toughness. With the increase in PLLA crystalline content, toughening becomes much easier to achieve. PLLA crystals are believed to provide a path for the propagation of shear yielding needed for effective impact energy absorption, and then, excellent toughening effect can be obtained when these crystals percolate through the whole matrix. This investigation provides not only a new route to prepare sustainable PLLA products with good impact toughness but also a fresh insight into the importance of matrix crystallization in the toughening of semicrystalline polymers with a flexible polymer.

Selective localization of titanium dioxide nanoparticles at the interface and its effect on the impact toughness of poly(L-lactide)/poly(ether)urethane blends

“…This observation is well consistent with the deteriorated impact toughness of the blends with high-concentration TiO 2 as mentioned above. In addition, our previous work has shown that the crystallinity of PLLA matrix may influence the impact toughness of PLLA/elastomer blend [53]. However, it can be disregarded completely in this work.…”

Fully bio-based, highly toughened and heat-resistant poly(L-lactide) ternary blends via dynamic vulcanization with poly(D-lactide) and unsaturated bioelastomer

“…7e, which is much larger than the optimum size (~0.75 μm) for highly toughened amorphous or low crystalline PLLA matrix [57]. The enhancement in molecular entanglement of the matrix by incorporation of PDLA is helpful for improving impact strength of PLLA [48], while higher crystallinity of the matrix is harmful, because it would make the matrix shear yielding more difficult [58]. The combination of the variations of phase morphology, molecular entanglement and matrix crystallinity accounts for the variation tendency of the blends versus PDLA content.…”

Brittleness and toughness of polymers and other materials

“…This is the most often used definition of toughness, although on occasions compression testing has been performed for an analogous purpose. The term "toughness" is also applied to the key result of impact testing, namely the energy necessary to cause fracture at high rates of force application [4,5]. Thus there exists fracture toughness, notch toughness, determined in impact testing for a predetermined geometry of the notch and testing method (e.g.…”